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[23.128.96.38]) by mx.google.com with ESMTPS id u9-20020a056a00124900b0068a5752a049si1299892pfi.96.2023.10.17.02.30.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Oct 2023 02:30:48 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.38 as permitted sender) client-ip=23.128.96.38; Authentication-Results: mx.google.com; dkim=fail header.i=@igalia.com header.s=20170329 header.b=bGnrI2i7; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.38 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (depot.vger.email [IPv6:2620:137:e000::3:0]) by fry.vger.email (Postfix) with ESMTP id B03CA8083DC9; Tue, 17 Oct 2023 02:30:28 -0700 (PDT) X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.10 at fry.vger.email Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234840AbjJQJaG (ORCPT + 19 others); Tue, 17 Oct 2023 05:30:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234966AbjJQJ3g (ORCPT ); Tue, 17 Oct 2023 05:29:36 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 47F21119 for ; Tue, 17 Oct 2023 02:28:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:MIME-Version:References: In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=Bv4UhAyma+StQ1C/srhttolaGUlSYmJrKK1FzAxXGo0=; b=bGnrI2i74XpILAOrXy08pbTd/v 81bMUL3IdoVDj6Bn0dsuwq+GforHlb+xY+LF8RrY2foCmwoMgFc+t7Oyp6z6N4sl6/nJ1aCYM1nqN 2ThxwX1I3zFVoBjU0mVJmu5Uljc14aHgdAWSITF+8T+9JvaNaEzdFL57sJJvSRU8RaFU+FIJwb5ZA DQ6S3DVsYafkafX3WrYvKpbdWdIVnptDnsugR+LKHn8lFfyEWTQYLT9LyKnO3aqdjEH/DXciYBOU9 Fgsg6X8+nHnDw+QuEMeYxc9Uxi8/7FRH2U2876fRjVxjZNXDlEw67P3Y+ZPuWhNbAu/fWs+sr/Ppe Qt8syUsw==; Received: from 167.red-81-39-185.dynamicip.rima-tde.net ([81.39.185.167] helo=localhost.localdomain) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1qsgNe-001ODF-Lc; Tue, 17 Oct 2023 11:28:50 +0200 From: =?utf-8?q?Andr=C3=A9_Almeida?= To: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: pierre-eric.pelloux-prayer@amd.com, =?utf-8?b?J01hcmVrIE9sxaHDoWsn?= , =?utf-8?q?Michel_D?= =?utf-8?q?=C3=A4nzer?= , "Randy Dunlap" , "Pekka Paalanen" , hwentlan@amd.com, kernel-dev@igalia.com, alexander.deucher@amd.com, christian.koenig@amd.com, joshua@froggi.es, Simon Ser , Pekka Paalanen , =?utf-8?q?Andr=C3=A9_Almeida?= Subject: [PATCH v7 5/6] drm/doc: Define KMS atomic state set Date: Tue, 17 Oct 2023 11:28:36 +0200 Message-ID: <20231017092837.32428-6-andrealmeid@igalia.com> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231017092837.32428-1-andrealmeid@igalia.com> References: <20231017092837.32428-1-andrealmeid@igalia.com> MIME-Version: 1.0 X-Spam-Status: No, score=-0.6 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on fry.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (fry.vger.email [0.0.0.0]); Tue, 17 Oct 2023 02:30:28 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1779994511317641028 X-GMAIL-MSGID: 1779994511317641028 From: Pekka Paalanen Specify how the atomic state is maintained between userspace and kernel, plus the special case for async flips. Signed-off-by: Pekka Paalanen Signed-off-by: André Almeida --- v7: - add a note that drivers can make exceptions for ad-hoc prop changes - add a note about flipping the same FB_ID as a no-op --- Documentation/gpu/drm-uapi.rst | 47 ++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst index 632989df3727..34bd02270ee7 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -570,3 +570,50 @@ dma-buf interoperability Please see Documentation/userspace-api/dma-buf-alloc-exchange.rst for information on how dma-buf is integrated and exposed within DRM. + +KMS atomic state +================ + +An atomic commit can change multiple KMS properties in an atomic fashion, +without ever applying intermediate or partial state changes. Either the whole +commit succeeds or fails, and it will never be applied partially. This is the +fundamental improvement of the atomic API over the older non-atomic API which is +referred to as the "legacy API". Applying intermediate state could unexpectedly +fail, cause visible glitches, or delay reaching the final state. + +An atomic commit can be flagged with DRM_MODE_ATOMIC_TEST_ONLY, which means the +complete state change is validated but not applied. Userspace should use this +flag to validate any state change before asking to apply it. If validation fails +for any reason, userspace should attempt to fall back to another, perhaps +simpler, final state. This allows userspace to probe for various configurations +without causing visible glitches on screen and without the need to undo a +probing change. + +The changes recorded in an atomic commit apply on top the current KMS state in +the kernel. Hence, the complete new KMS state is the complete old KMS state with +the committed property settings done on top. The kernel will try to avoid +no-operation changes, so it is safe for userspace to send redundant property +settings. However, not every situation allows for no-op changes, due to the +need to acquire locks for some attributes. Userspace needs to be aware that some +redundant information might result in oversynchronization issues. No-operation +changes do not count towards actually needed changes, e.g. setting MODE_ID to a +different blob with identical contents as the current KMS state shall not be a +modeset on its own. As a special exception for VRR needs, explicitly setting +FB_ID to its current value is not a no-op. + +A "modeset" is a change in KMS state that might enable, disable, or temporarily +disrupt the emitted video signal, possibly causing visible glitches on screen. A +modeset may also take considerably more time to complete than other kinds of +changes, and the video sink might also need time to adapt to the new signal +properties. Therefore a modeset must be explicitly allowed with the flag +DRM_MODE_ATOMIC_ALLOW_MODESET. This in combination with +DRM_MODE_ATOMIC_TEST_ONLY allows userspace to determine if a state change is +likely to cause visible disruption on screen and avoid such changes when end +users do not expect them. + +An atomic commit with the flag DRM_MODE_PAGE_FLIP_ASYNC is allowed to +effectively change only the FB_ID property on any planes. No-operation changes +are ignored as always. Changing any other property will cause the commit to be +rejected. Each driver may relax this restriction if they have guarantees that +such property change doesn't cause modesets. Userspace can use TEST_ONLY commits +to query the driver about this.